1. Field of the Invention
The present invention relates to a laminated piezoelectric element such as an actuator, a piezoelectric buzzer, a sound component and a sensor.
2. Description of the Related Art
Typical examples of the piezoelectric element may include an actuator. The actuator taking advantage of the displacement generated by the piezoelectric effect as the mechanical driving source has such advantages that the actuator is small in electric power consumption and in heat release, satisfactory in response, and capable of being reduced in size and weight; thus, the actuator has come to be applied to a wide variety of fields. Piezoelectric ceramic compositions to be used in such an actuator are required to be high in piezoelectric properties, in particular, large in piezoelectric strain constant. As piezoelectric ceramic compositions satisfying such properties, there have been developed, for example, a ternary piezoelectric ceramic composition containing lead titanate (PbTiO3), lead zirconate (PbZrO3) and lead zincate niobate [Pb(Zn1/3Nb2/3)O3], a piezoelectric ceramic composition in which the Pb in the above-mentioned ternary piezoelectric ceramic composition is partially substituted with Sr, Ba, Ca or the like, and other piezoelectric ceramic compositions.
However, these conventional piezoelectric ceramic compositions require sintering at relatively high temperatures of the order of 1100 to 1250° C., and undergo sintering in an oxidative atmosphere; consequently, for example, in laminated actuators or the like in which internal electrodes are simultaneously sintered, it is necessary to use as electrode materials noble metals (such as Pt and Pd) that are high in melting point and are not oxidized even when sintered in an oxidative atmosphere. As a result, the increase in cost is caused to offer an obstacle to price reduction of manufactured piezoelectric elements.
Under these circumstances, the present applicant has proposed in Patent Document 1 to enable low-temperature sintering by adding a first additive containing at least one selected from Fe, Co, Ni and Cu and a second additive containing at least one selected from Sb, Nb and Ta to the above-mentioned ternary piezoelectric ceramic compositions, and consequently to make usable low-price materials such as a Ag—Pd alloy for internal electrodes.
Patent Document 2 also discloses a proposal that the sintering at 900° C. or lower is made possible and the noble metal proportion in the internal electrodes is reduced by adding Ag2O in a proportion of 0.005 to 0.03% by weight to a perovskite composition represented by Pba{Zrb.Tic.(Ni1/3Nb2/3)d.(Zn1/3Nb2/3)e}O3 wherein 1.000≦a≦1.020, 0.26≦b≦0.31, 0.34≦c≦0.40, 0.10≦d≦0.35, and 0.07≦e≦0.14.
[Patent Document 1] Japanese Patent Laid-Open No. 2004-137106
[Patent Document 2] Japanese Patent Laid-Open No. 2003-238248